I just got my 1948 D2 Kitty home that was given to me and the engine is stuck so I pulled the injectors and pre-combustion chambers out to spray PB Buster in in hopes to break it loose. On the #2 cylinder the pre-combustion chanber has some deep pitting.
What areas is the pitting not acceptable?
Are they a standard part or unique by year?

It's not quite that easy as there are different style shape chambers used on the same models. In general they tend to corrode more towards the bottom with deep pitting compromising the thread and seal area. If you are suspicious it would be wise to replace them.

I have a book from Cat on all the cooling system problems and causes and it shows the prechambers pitting problem.There are a few causes listed but not necessary to list them all but the bottom line is using acceptable water and a correct addative for the problem.The main thing would be to drain and flush out the system best you can and then refill with new water and antifreeze and the correct addative then.I have seen at the dealer liners that were eaten nearly through from cavation too so there is an addative for this problem that Cat sells.

I have repaired chambers by welding.Its amazing what damage water can do.Always use additives and antifreeze.The chamber I removed from my D2 many years back was in a right mess,it looked if it had a bight taken out of it.

Martyn, it,s not uncommon to see this happen to chambers and liners as I mentioned before and good maintenance is the main thing and addatives put in the coolant to prevent it.At the dealer I seen it all the time and not old engines either but some nearly new ones and the cavatation was the culprit usually with the liners.